Automatic submarine trencher

ABSTRACT

An automatic trencher is provided for entrenching a pipeline in the bed of a body of water. The trencher is adapted to ride over the pipeline and includes one or more trenching tools which cut away the formation of the bed to form a single trench therein for receiving and burying the pipeline. Power and control signals are supplied by a flexible cable coupling the trencher with an accompanying overhead marine vessel. This power is used to move the trenching tools, to advance the trencher along the path of the pipeline as the trench is being formed, and to energize surveillance apparatus. Depending on the type of soil, tools of various configurations can readily be interchanged while the trencher is submerged. Piston-type hydraulic pump-motor combinations rotate the tools and propel the trencher along the desired path. Means responsive to the fluid pressure in the pumps automatically maintain the power output at the tools substantially constant within a wide range of load variations, thereby greatly increasing both the efficiency of the tools and the speed of the trenching operation.

United States Patent Breston et al.

[451 June 20, 1972 1 AUTOMATIC SUBMARINE TRENCHER [72] lnventors:Michael P. Breston; Ray D. Kellberg, both of Houston, Tex.

[73] Assignee: Fluor Corporation, Los Angeles, Calif.

[22] Filed: Sept. 4, 1970 [21] Appl.No.: 69,566

Primary Examiner-Jacob Shapiro Attorney-Michael P. Breston and Alfred B.Levine ABSTRACT An automatic trencher is provided for entrenching apipeline in the bed of a body of water. The trencher is adapted to rideover the pipeline and includes one or more trenching tools which cutaway the formation of the bed to form a single trench therein forreceiving and burying the pipeline. Power and control signals aresupplied by a flexible cable coupling the trencher with an accompanyingoverhead marine vessel. This power is used to move the trenching tools,to advance the trencher along the path of the pipeline as the trench isbeing formed, and to energize surveillance apparatus. Depending on thetype of soil, tools of various configurations can readily beinterchanged while the trencher is submerged. Piston-type hydraulicpump-motor combinations rotate the tools and propel the trencher alongthe desired path. Means responsive to the fluid pressure in the pumpsautomatically maintain the 21 Clailm, 13 Drawing Figures PATENTEDJum1912 3.670514 SHEET 10F 5 FIG. 1

MICHAEL P. BRESTON RAY D. KEILBERG INVENTORS BY MICHAEL P BRESTONATTORNEY PKTE'N'TEDaunzo m2 3 5 70,514

sum 2 or s MICHAEL R BRESTON RAY D. KEILBERG I N VEN TORS BY MICHAEL P.BRESTON ATTORNEY PATENTEMm m2 3,670,514

sum 3 or s ELECT RIC POWER MONITOR 8 CONTROL FIG. 4 MICHAEL P. BRESTONRAY D. KEILBERG INVENTORS BY MICHAEL P. BRESTON ATTORNEY PATENTEDJmo1912 3.670. 5 .1 4

sum u or s MICHAEL P. BRESTON RAY D. KEILBERG INVENTORS BY MICHAEL P.BRESTON ATTORNEY PATENTEDJUN 20 I972 3. 6 70.514

SHEET 5 0f 5 MICHAEL P. BRESTON RAY D. KEILBERG INVENTORS BY MICHAEL F?BRESTON ATTORNEY BACKGROUND OF THE INVENTION Prior art trenchers forentrenching pipelines are known to have serious drawbacks. Sometrenchers, for example, are self-propelled on hydraulically operatedwheels which ride on the coating of the pipeline. In practice it isdifficult to avoid damaging the coating and creating cracks thereinthrough which sea water can reach the metal pipe and corrode its wall.To repair a damaged section of an underwater pipeline is extremelyexpensive. Also, since the trencher must work in hard as well as softsoils, the loads on the cutters vary over a considerable range. Theprime movers of known trenchers are accordingly provided with complexcontrol mechanisms which often require the shifting of gears, clutches,control knobs, throttles, etc. To prevent the cutters from stalling, theprime movers (diesel engines on the floating vessel) are adjusted todeliver to the cutters considerably more energy than is actuallyrequired by them. Among the consequences of the above are: greater fuelconsumption, and faster wear of the blades on the cutters. Thereplacement of the cutters (or their blades) is very time-consuming andexpensive. These and other drawbacks prevent prior art trenchers fromcarrying out the entrenching of a pipeline at fast rates of speed evenin moderately soft soils.

SUMMARY OF THE INVENTION It is therefore a general object of theinvention to provide a trencher, for entrenching a pipeline under thebed of a body of water, intended to obviate known problems, includingthe type previously described.

It is a particular object of the invention to provide such trencherswherein the cutters are easily interchangeable to allow the depth andwidth of the trench to be readily varied. It is another object of theinvention to provide a submerged trencher wherein a substantiallyconstant horsepower is developed by the trenching tools as the trenchingoperation progresses. It is a further object of the invention to providean apparatus for entrenching pipe wherein the trenching tools aresubjected to a minimum of wear and tear, thereby making it possible forthe trenching operation to progress at a faster rate and for a longerperiod of time.

It is yet another object of the invention to provide a trencher whereinthe trenching tools are rotated by pistontype hydraulic motors.

It is a further object of the invention to provide a trencher whichrides over the pipe as it cuts the trench in such a manner as to:minimize loading the pipe, prevent damaging its outer coating, andreceive continuous propulsion power from an indication of the positionof the trencher relative to the pipe.

An apparatus for digging trenches on the bed of a body of water,according to a preferred embodiment of the invention, utilizes afloating marine vessel movable forwardly along a longitudinal pathrelative to the pipeline. The trencher includes a frame supported byground-engaging means adapted for rolling or sliding motion on thesurface of the bed of the body of water. The rolling motion is obtainedfrom submerged propulsion means. Rotatable cutters, adapted for cuttinga single trench in the bed, are connected to the frame by coupling meansselectively adjustable in both horizontal and vertical directions.

In order to guide the ground-engaging means relative to the pipeline,sensor means coupled to pipe-engaging means provide propulsion controlsignals which are used to selectively control the speed and torque ofthe hydraulic motors driving the ground-engaging means.

In the preferred embodiment, the ground-engaging means includeself-propelled rolling tracks which can be easily disconnected from theframe and replaced with sliding skids. The trencher is then towed on thebed by a floating vessel to cause a trench to be cut therein.

Further apparatus aspects of the invention reside in the provision ofvertical guide rollers connected with the groundengaging means forgently guiding the ground-engaging means along the path of the pipeline.

Important apparatus aspects of the invention reside in the provision: ofa prime mover which can be allowed to run at a constant speed therebyefficiently utilizing its full output power capabilities, of piston-typemotors for rotating the cutting tools, and of pressure transducersefiective to continuously and automatically control the angular velocityand the torque of the cutting tools.

Other aspects reside in the provision of removable tracks which can bereplaced with interchangeable skids to allow the trencher to becometowed.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and. 2 diagrammaticallyillustrate a preferred hydraulic network used to rotate the cuttingmeans;

FIG. 3 is a side view of the pipe entrenching system in accordance witha preferred embodiment;

FIG. 4 is a top view of the system shown in FIG. 3;

FIG. 5 is a side view of the system shown in FIG. 3;

FIG. 6 is a front view of the system shown in FIG. 3;

FIG. 7 is a detail view of a portion of the track propulsion means;

FIG. 8 illustrates another embodiment of a cutter means;

FIG. 9 is a detail view of a portion of power means applied to thecutter means;

FIG. 10 illustrates the manner of detachably coupling and securing acutting means;

FIG. 1 1 is a side view, partly in section, illustrating the manner ofdisplacing a guide roller relative to the pipeline;

FIG. 12 is a side view of an entrenching system sliding on skids; and

FIG. 13 is a partial view of a skid shown in FIG. 12.

DETAILED DESCRIPTION OF THE HYDRAULIC POWER SUPPLY FOR THE CUTTERELEMENTS In FIGS. 1, 2 there is shown a hydraulic power supply 19 withautomatic power output control means. Power supply 19 includes a dieselengine 20 having a shaft 22 coupled by a coupling device 24 to the shaft26 of a suitable hydraulic pump 28. Various types of hydraulic pumps arecommercially available. An axial-piston type pump is preferred for theload requirements of the cutter elements. An axial-piston type pumpincludes an odd number of pistons 34 spaced circumferentially. A baseplate 36 is connected to the pistons 34 by connecting rods 38. The baseplate 36 is flexibly coupled to shaft 26 by a universal joint 37.Rotation of shaft 26 causes pistons 3 base plate 36 and rods 38 torotate together as an assembly about the axis of shaft 26. Linearmovement of a control rod 44 causes the base plate 36 to tilt relativeto the axis of shaft 26. When the base plate 36 tilts, the connectingrods 38 change the strokes of pistons 34.

In operation of pump 28, when base plate 36 is in a plane perpendicularto the axis of shaft 26, the stroke of pistons 34 is zero with no fluidcirculating through the pump. By tilting the base plate, a pumpingaction is created. Fluid (typically oil) is drawn into thepistonscylinders during one half revolution, and forced out ahead of thepistons during the other half revolution. The greater the tilt angle ofthe base plate, the greater the stroke of the pistons and hence, thegreater the volume pumped by the pump. The direction of fluid flowthrough the pump can be reversed almost instantaneously by tilting theinclinable base plate 36 in the opposite direction relative to the axisof shaft 26.

Pump 28 feeds two main hydraulic lines 46, 48 across which are connecteda number of identical motors 50, each shaft of each motor ismechanically coupled to a rotating element 52. Since the speed ofrotation of element 52 is usually considerably les than the operatingspeed of motors 50, a conventional planetary reduction gear 53 isinterposed to provide an appropriate drive ratio therebetween.

It will be appreciated that the internal construction of motors 50 andof pump 28 are exactly identical.

Direction of rotation of motors 50 is controlled by the direction offluid flow through the motors and, hence, by the position of the baseplate 36 relative to the axis of shaft 26 in pump 28. Since the baseplate is always tilted at least a minimum angle, any fluid flow througha motor 50 will impart rotation to its shaft 26. To better bring out thesimilarity in design between the pump 28 and motors 50, their internalparts are assigned the same reference characters, with the referencecharacters in the motors followed with a prime. Since the base plate 36is always tilted at least a minimum angle, any fluid flow through amotor 50 will impart rotation to its shaft 26'. The angular velocity ofshaft 26' can be continuously varied by changing the tilt angle betweena minimum and a maximum angle, and vice versa. When the tilt of baseplate 36 is at a minimum, the pistons stroke is the shortest; less fluidvolume is needed to rotate the inside motor assembly, and the motor hasits maximum speed and minimum torque. Thus the smaller the minimum angleof tilt is, the greater the maximum speed will be. On the other hand,when the tilt is at its maximum angle, the pistons stroke is longest;more fluid is needed to rotate shaft 26'; and the motor has it s maximumtorque and minimum speed.

Motors 50 are made to automatically and continuously develop, for agiven input power, a substantially constant output horsepower whilehandling the load on element 52. The input power applied to a motor 50by pump 28 is directly related to the fluids velocity and pressure. Thetorque requirements of the load on element 52 govern the pressure inmotor 50 and, hence, in supply lines 46, 48. The fluids pressure in line46, 48 is continuously monitored by a pressure transducer 58 whichincludes a calibrated spring 62, a piston 64 having a rod 66. Since thepressure can be higher in either of lines 46 and 48, there is providedbetween the lines a shuttle valve 68 which supplies to a line 70 eitherthe pressure of line 46 or of line 48 whichever is greater.

The primary actuator for pump 28 is a low pressure, airoperated cylinder74 whose piston 76 is coupled by a rod 78 to a hydraulic force amplifier72 which is coupled to rod 44. When piston 76 becomes displaced, baseplate 36 is caused to tilt-and thereafter amplifier 72 keeps the controlrod 44 in place until another command from the throttle of pump 28causes air pressure to be admitted into air cylinder 74 thereby raisingor lowering piston 76 therein. Thus the force amplifier 72 transmits thedisplacement of rod 78 to the control rod 44, in response to an aircommand signal which is greatly amplified by the amplifier 72 to developthe considerable force required to tilt the base plate 36.

The base plate control system of each motor 50 also includes a hydraulicamplifier 72' functioning in the manner above-described. In the case ofthe motors, however, each pair of amplifiers 72' is actuated by theoutput force from the pres- .sure transducer 58. The spring 62 is suchthat only pressures above a minimum pressure level can push piston 64down against the spring's force. The minimum tilt of base plate 36' inmotor 50 provides a sufficient torque on shaft 26' to handle light loadson element 52.

As previously mentioned, an increase in load torque causes acorresponding increase in the main line fluid pressure. When the linepressure exceeds the minimum pressure level on, say, line 46, the vane69 in shuttle valve 68 will move down allowing the line 46 pressure toexert a force, through line 70, on piston 64 and move it down. Adownward displacement of piston 64 causes the base plate 36 to tilt.

A series of check valves is connected across the two main circuit lines46, 48 at a point near pump 28: two check-valves 120 and twocheck-valves 122. A pressure relief valve 124 is mounted between thejunctions of the check-valves to allow pressure above a set minimum topass from the intake line to the exhaust line around the pump 28. Thusif excess pressure should accidentally build up in either of the maincircuit lines 46, 48, it will enter one of the intake check-valves 120,pass through the pressure relief valve 124, and exit through theopposite exhaust check-valve 122. An air-operated cross-over valve 126is provided between the intake and exhaust checkvalve lines 127 and 129,respectively. Valve 126 becomes automatically actuated, whenever pump 28is in its neutral (nonpumping) position, to allow cross-over between themain circuit lines 46, 48. The main hydraulic input is into the exhaustcheck-valve line 129. From there the super-charged pressure passesthrough that valve 122 which is connected to the line (46 or 48) havingthe lower pressure.

When the element 52 is rotating, circulation through the main lines 46,48 is counter clockwise. An air-operated valve 148 can shut off fluidcirculation to the motors in order to make available the prime mover 20and pump 28 to operate other auxilliary machines. The air cylinder 74 isactuated through a throttle valve 75 having a valve spool 77. When spool77 is in its neutral position, pump 28 delivers no fluid to the motors50. The flow of fluid through pump 28 depends on the position ofthrottle valve 75 relative to its neutral position. In operation of thepower supply 19, the prime mover engine 20 may be set to run at aconstant speed (corresponding to maximum torque) thereby conservingfuel. Air cylinder 74 is then operated to cause pump 28 to deliver adesired output volume into the main hydraulic lines 46, 48. When theline pressure is less than the minimum pressure level, the base plates36 and in motors 50 will be at their minimum tilt positions and themotors will have a sufficient torque capability to handle average loads.For greater loads the pressure on line 48 rises above the minimumpressure level thereby compressing spring 62. The down movement ofpiston 64 causes the base plate 36' to tilt by an angle corresponding tothe displacement of piston 64. This results in a decrease in the speedof element 52 and in a corresponding increase of its torque. Thus, aload change will cause through transducer 58 an instantaneous decreasein speed and increase in torque, or vice versa. The design factors aresuch that the output horsepower of each motor 50 remains substantiallyconstant over the expected load range.

It will therefore be appreciated that the operator by merely controllingthe position of valve spool 77 in-air valve 75 can set the base plate 36in pump 28 in neutral position (no pump- When base plate 36' tilts inresponse to an increase in line pressure, the speed of shaft 26'decreases and its torque increases so that the horsepower developed bymotor 50 remains substantially constant. The magnitude of this power isdetermined by the volume of fluid pumped through the motor by pump 28.When the load torque is at its expected maximum level, the line pressurereaches its maximum value causing the base plate 36' to assume itsmaximum tilt angle. The speed velocity of shaft 26' is then at a minimumand its torque at a maximum.

ing) or on either side of the axis of shaft 26 (pumping in eitherclockwise or counterclockwise direction). The actuation of air cylinder74 through valve 77 is the main throttle control which needs to bemanipulated by the operator. Consequently, the gear ratio between thespeed of pump 28 and the speed of motors 50, is automatically selectedby the load on element 52.

GENERAL DESCRIPTION OF THE TRENCHING SYSTEM Referring to FIGS. 3-11,there is shown a preferred embodiment of a trenching system, generallydesignated as 200, which utilized a vessel 202 movable in the generallongitudinal direction of a pipeline 204 desired to be buried in the seabed 206. Vessel 202 is coupled through an umbilical cable 208, to atrencher machine, generally designated as 210. The umbilical cable 208has an outer flexible jacket within which are housed flexible linessupplying fluid power, electric power,

, and control signals to and from the trencher 210. The trencher 210 isbuilt on a frame 212, which can be towed or selfpropelled. A trenchingapparatus 214 is carried by and is movable relative to frame 212. Thetrencher 210 rides above the pipeline 204 and with the use of rotatablecutter elements or tools 216 excavates a trench 218 in the formation ofthe sea bed 206. Front and rear guide rollers 220, 222 are verticallydisposed on frame 212 and gently guide the frame along the pipeline 204.Frame 212 is of the open frame design and supports areceiving-and-transmitting unit 240 housed in an enclosure 242 which ispressure compensated by a pressure compensator 244. Compensator 244makes the pressure inside enclosure 242 substantially equal to thesurrounding outside water pressure. Unit 240 receives the umbilicalcable 208 through a flanged port 241. Extending above frame 212 is atripod 246 which supports a rotatably mounted television monitor camera248, a pivotally mounted hydraulic cylinder 250, and a plurality ofhigh-intensity light beams 252.

The Propulsion System Frame 212 is propelled on tracks 224 and 226. Eachtrack is independently driven by a power unit 228 (FIG. 7) having ahydraulic motor 230. The shaft 232 of motor 230 is coupled to a driveshaft 234 via a chain 231 riding on sprockets. Shaft 234 is coupled to adrive shaft 229 through an intermediate shaft 402 which, in turn, iscoupled to shafts 229, 234 through detachable coupling devices 235, 237,respectively. The free end of shaft 229 is fixedly secured to a drivesprocket 236 which provides the necessary propulsion to track 224 ortrack 226. A plurality of idler sprockets 238 are also provided; theexact number and the spacing of the idler sprockets will vary with thelength of the track 224. The power unit 228 is housed in apressure-compensated enclosure 414 and shaft 234 extends outwardlytherefrom through a dynamic seal 415 in the side wall 412. Drive shaft229 is supported by a detachable bracket 254 which is secured to frame212 by bolts 256. Shaft 229 is joumaled in a sleeve bearing 400extending through bracket 254. Enclosure 414 is disposed immediatelybelow the receiving unit 240. It will be appreciated that through theside wall (not shown), opposite to the side wall 412, extends anothershaft 234 to similarly power track 226. Since the construction issymmetrical, the description is limited whenever possible to thecomponents used in one half of the trencher 210.

Under certain operating conditions, it may be desirable to tow frame212. In that event, track 224 can be easily disconnected by removing thedetachable bracket 254, disconnecting coupling devices 235 and 237, andsubstituting for bracket 254 a skid sub-assembly 258. Sub-assembly 258is secured to frame 212 by the same bolts 256. Each skid 258 is towed bya towing cable 257 or 259 depending on the direction of travel.

The Trenching Apparatus The trenching apparatus 214 includes a powerdrive unit 260 housed in an enclosure 262 which is pressure compensatedby a compensator 264. Enclosure 262 is supported by and fixedly attachedto a frame 265 secured to a horizontal pivot shaft 266 joumaled forrotation on frame 212. Pivotally supported on a pair of vertical pivots267 are arms 268, 270. Rod 251 of hydraulic cylinder 250 is pivotallyconnected by a clevis 167 to frame 265. Two hydraulic cylinders 272, 274are pivotally connected between frame 265 and arms 270, 268,respectively. When the rods of cylinders 272, 274 are extended (byremote control operation through the umbilical cable 208), arms 268, 270rotate away from a vertical plane extending through the longitudinalaxis of the pipeline 206. Conversely, when these rods are caused to moveinside cylinders 262, 274 the arms 268, 270 move toward the pipeline.When arms 268, 270 are fully rotated inwardly they are detachablycoupled together by a locking mechanism 276 having male and femaleconnector parts 278, 280 joined together by a removable pin 282 or by aremotely operated lock (not shown).

Mounted near the ends of arms 268, 270 are gear boxes 284, 286,respectively (FIGS. 4, 10). Each gear box is completely enclosed andpressure compensated by a compensator 287. Connected to the top walls ofgear boxes 284, 286 are flanged connectors 288, 290, respectively. Toeach connector is coupled a water hose 289. Rotatably supported on theframes of arms 268, 270 are diametrically opposed rollers 292 whosefunction is to protect the coating of the pipeline. The rollers areconveniently made of a resilient material such as urethane. Each of arms268, 270 is provided with one or more jet assist suction tubes,generally designated as 296. Each suction tube 296 includes a horizontaltube portion 298 and a vertically slanted tube portion 300. Each jetassist tube 296 receives high pressure water through a line 302extending from the unit 240.

As can be best seen from FIG. 11, each roller 220 or 222 rides on a rail22] via upper and lower rollers 223, 225 rotatably mounted on a bracket227 having a pressure-compensated enclosure 229. Roller 220 is rotatablymounted on a shaft one end of which is fixedly secured to a lowerbracket 181 and its other end extends through a port 182 which has adiameter slightly greater than the outer diameter of shaft 180. A piston183 is operatively coupled to a spring 184 which exerts a force on aload cell 185. Load cell 185 may include one or more strain gauges whichare connected to the floating vessel 202 through the umbilical cable208. A remotely operated hydraulic cylinder 219 is pivotally connectedto the frame of bracket 227 for moving roller 220 or 222 away from ortoward the pipeline.

The cutters can assume various configurations depending on the cuttingaction, the nature of the soil being excavated, are the desiredgeometrical configuration of the trench. As can be best seen in FIGS. 5,6, particular type cutters 310, 312 have a hollow vertical shaft 314from which extend a plurality of substantially C-shaped blades 316. Eachdiametrically opposite pair of blades 316 can be made into a unitaryconstruction fixedly or detachably secured to shaft 314. The detachablecoupling of the blades to shaft 314 is preferred in order to allow forthe easy replacement of worn out blades. The top end of each shaft 314forms an enlarged head 318 (FIG. 10) which serves as a female connectorfor receiving the lower end 320 of a stub-shaft 340. A bolt 168 secureshead 318 to shaft 340. Shaft 340 extends through two dynamic seals 341,343 in the frame of arm 268.

Inside gear box 284 is a beveled gear arrangement 342 which serves tocouple the top end 321 of the vertical shaft 340 to a horizontal driveshaft 334. Shaft 334 is journaled in a dynamic seal 338.

With particular reference to FIGS. 1, 5, 9, and 10 shaft 334 is coupledto an intermediate drive shaft 330 through a universal joint 336, andshaft 330 is'coupled to the shaft 52 (FIG. 1) through a universal joint332.

The piston-type hydraulicmotors 50 have their shafts 26' coupled toshaft 52 through the planetary reduction gear mechanism 53, which canconveniently include two chains 13, 16 riding on two pairs of sprocketsll, 12 and 14, 15, respectively.

In FIG. 8 is shown a different configuration of a cutter tool, generallydesignated as 322. Tool 322 is fonned from a tubular member 324 to theouter cylindrical periphery of which are secured (fixedly or detachably)a plurality of blades 326 preferably in the form of scoops. Other bladeconfigurations, such as the C-shaped blades 316, can also be employed.The bottom end of tube 324 is provided with a plurality of verticallyextending teeth 328 to facilitate the penetration of cutting tool 322into the formation of the sea bed. The connecting mechanism fordetachably securing the cutter 322 to the drive shaft 340 is identicalto that shown and described in connection with the coupling of tool 310to the drive shaft 340.

With certain cutters it may be desired to jet water through the hollowshaft 314 or the tube 324 by forcing water through the hose 289connected to the flanged connector 288 (FIG. 10). The high-waterpressure will exit through the bottom opening of shaft 314 or throughports 325 in the outer wall of tube 324.

On the marine vessel 202 is provided the diesel engine 20 for drivingthe hydraulic pump 28. Another prime mover or diesel engine 170 drives ahydraulic pump 171 which feeds hydraulic fluid through lines 172, 173 tothe track-propulsion motors 230. Other hydraulic and air lines (notshown) extend from a fluid supply source 21 through the umbilical cable208 for actuating the remotely operated hydraulic and air devices suchas 250, 272, 274, and 219, etc., previously described.

Electric power is applied to the television camera 248, thehigh-intensity light beams 252, and to other electrically operatedinstrumentalities used on or in connection with the trencher 210. Thepower and signals are fed through cables 174, 175 from an electric powermonitor-and-control system, generally designated as 176.

DESCRIPTION OF THE OPERATION OF THE TRENCl-IER SYSTEM Prior to loweringthe trencher 210 above the pipeline 204, cylinders 272, 274 are extendedto their maximum length thereby moving arms 268, 270 away from eachother. Arms 268, 270 rotate on pivots 267. Cylinder 250 is thencontracted to cause the rotation of frame 265 in a clockwise directionas viewed in FIG. 5. Cylinders 219 are then extended to allow for amaximum separation between the oppositely disposed guide rollers 220,222.

A suitable crane (not shown) on the deck of vessel 202 is used to lowerthe trencher machine 210 above pipeline 204. Divers will be used toassist during the lowering of machine 210. When the use of divers is notfeasible or desirable, other conventional control and guidance means canbe employed. After frame 212 is disposed above pipeline 204, there maybe a need to center the machine relative to the vertical plane extendingfrom the longitudinal axis of the pipeline. The centering isaccomplished by rotating tracks 224 and/or 226 independently and/orsimultaneously. With the tracks resting well on the sea bed 206, theirpositions relative to the pipeline are monitored by observing thesignals received from the load cells 18S.'A signal is received from aload cell 185 when its corresponding guide roller 220 engages the wallof pipe 204. The force exerted by the pipe on roller 220 or 222 istransmitted to the load cell 185 by the piston 183 and spring 184. Asthe centering of the frame 212 progresses, the operator graduallycontracts cylinders 219 until all four guide rollers gently engage thepipe 204.

Thereafter motors'50 are energized to cause the rotation, in oppositedirections, of cutters 310, 312. As cutters 310, 312 cut away portionsof the soil formation, cylinder 250 is gradually extended until thecutters assume both the desired angle relative to the vertical, and thedesired penetration into the trench. Cylinders 272, 274 are thencontracted to cause arms 268, 270 to movetowards each other until thelocking mechanism 276 can be locked with pin 282. Pin 282 can beinserted by a diver or it can be remotely operated.

During the lowering of the cutters 310, 312 into the sea bed formation,the tracks 224, 226 are simultaneously propelled forward to provide anopening for the jet assist suction tubes 296. High pressure water fromlines 302 is ejected through the horizontally extending tubes 298 sothat a relatively low pressure (pumping action) is created in each ofthe vertically extending tubular portions 300. Tubes 300 suck up thedebris of the cutting operation and eject them through the tubularportions 298 which extend past tracks 224, 226 to prevent theaccumulation of debris in the path of travel of the tracks.

The speed with which the trencher 210 progresses depends on how fast thecutters 216 will cut away from formation of bed 206. Since the densityof the soil varies from location to location, different loads will beimposed on the cutters. The speed and torque of the piston-typehydraulic motors 50 will be automatically varied by the pressure sensingdevices 58 (as previously described in connection with the hydrauliccircuit of FIGS. 1, 2) to maintain the output power at the cutters 216substantially constant. Since the speed and torque of the cutters areautomatically varied, depending on the density of the soil encountered,it will be appreciated that minimum wearand-tear is imposed on theblades 316, and, hence, the blades will require less frequentreplacement thereby allowing longer uninterrupted trenching operations.

After the trencher 210 is properly centered about the pipeline with theselectively adjustable coupling devices secured and locked in theirproper positions, the track propulsion system will be operated, in amanner as-to maintain the ground-engaging. means (tracks or skids) alongtheir desired course of travel, by selectively and independentlycontrolling the speed and torque developed by the propulsion motors 230.Should the ground-engaging means not follow the desired course, the sideguide rollers 220 or 222 will produce signals from'their load cells 185,which signals will be transmitted through the umbilical cable 208 to themonitor-and-control station 176 on the deck of vessel 202. These signalare used to properly control the propulsion system. The control can bemanual or automatic as will be apparent to those skilled in the art.

SUMMARY OF THE ADVANTAGES The apparatus of the present inventionprovides considerable advantages in carrying out pipe entrenchingoperations on the bed of a body of water.

Particular advantages are provided by the sensing means coupled to theside guide rollers which gently roll on the coating of the pipe todetermine the desired path of travel for the ground-engaging means. Thesensing means provide a continuous remote indication for persons on thevessel of the actual position of the pipeline on the sea bed relative tothe frame. I

A very significant advantage is provided by the piston-type motors whichautomatically vary the speed of the cutting tools to maintain the propertorque for the type of soil being excavated. l

Another significant advantage lies in the provision of readilyinterchangeable cutting means for various types of soil and for variousgeometrical configurations of the trench.

Although the invention has been described with reference topreferredembodiment's, it will be apparentto those skilled in the artthat additions, deletions, modifications, substitutions and otherchanges, not specifically described or illustrated in connection withthe preferred embodiments, may be made which fall within the scope ofthe appended claims.

What we claim is: l

1. In a trenching system for cutting a trench in the bed of a body ofwater and including: a frame, ground-engaging means coupled to saidframe and adapted to move on said bed, at

' least one axially extending support ann, movable coupling meanscoupling said arm to said frame for selectively moving said support armrelative to said frame, and at least one rotatable cutter meansextending downwardly from said support arm, the improvement comprising:7

hydraulic power means including a prime mover, a hydraulic pump, atleast one hydraulic motor, a hydraulic circuit operatively coupling saidpump to said motor to energize said motor with hydraulic fluid, meanscoupling the output shaft of said motor to said cutter means to rotatesaid cutter means when said motor is energized, and control meansresponsive to the pressure in the hydraulic circuit for automaticallyadjusting the power output of said motor. a

motor having a speed control element, said control means is coupled tosaid speed control element to automatically vary the speed of said shaftin ac- 2. The system of claim 1 wherein said motor is a piston-type apair of self-propelled tracks, and

at least one hydraulic motor coupled to each track for moving saidtracks, independently or simultaneously, on said bed toward or away fromthe direction of the trench being cut.

4. The system of claim 3 wherein said frame moves over a pipeline andfurther including:

roller means rotatably supported on said frame and adapted to rollinglyengage said pipeline at horizontally spaced locations for guiding saidframe on said pipeline. 5. The system of claim 4 and further including:sensor means coupled to said roller means for monitoring the position ofsaid frame relative to said pipeline, and

monitoring means adapted to be positioned on said vessel and connectedto said sensor means, said monitoring means being responsive to thesignals produced by said sensor means for providing an indication of theposition of said frame relative to said pipeline.

6. The system of claim 5 wherein said ground-engaging means includeself-propelled track means remotely operated from said vessel independence on said monitored signals received from said sensor means.

7. The system of claim 6 wherein said cutter means extend downwardly ata predetermined depth below said ground-engaging means whereby forwardmotion of said frame causes said cutter means to cut a trench in saidbed.

8. The system of claim 7 and further including:

at least another axially extending support arm,

movable coupling means coupling said am to said frame for selectivelymoving said support arm relative to said frame,

means movably interconnecting said arms for selective movement ofsaid'arms away from and toward each other, and

least another rotatable cutter means downwardly from said anothersupport arm. 9. The system of claim 8 wherein said frame extends rearatextending wardly of said cutting means and is adapted for motion along 7said pipeline, and

pivot means carried on said frame for imparting pivotal motion to saidarms about a generally horizontal axis.

10. The system of claim 1 wherein said ground-engaging means is a skidadapted for sliding movement on the surface of said bed.

11. The system of claim 1 wherein said cutter means comprises a tubularmember having outwardly extending, generally C-shaped blades thereon.

12. The system of claim 13 wherein said blades are in the form ofscoops.

13. The system of claim 4 wherein said roller means are movablysupported on said frame, and

means for selectively positioning said roller means on said framerelative to said pipeline. 7

14. The system of claim 11 wherein said cutter means are detachablysecured to their respective arms.

15. The system of claim 14 wherein said tubular member is hollow andfurther including:

high-pressure water means connected to said tubular member to facilitatethe trenching operation. 16. A trenching system for cutting a trench inthe bed of a body of water including:

a frame for moving over a pipeline, roller means rotatably supported onsaid frame and adapted to rollingly engage said pipeline at horizontallyspaced locations for guiding said frame on said pipeline;

ground-engaging means coupled to said frame and adapted to move on saidbed;

at least one axially extending support arm,

movable coupling means coupling said arm to said frame for selectivelymoving said support arm relative to said frame;

at least one rotatable cutter means extending downwardly from saidsupport arm;

said ground-engaging means including:

a pair of self-propelled tracks,

at least one hydraulic motor coupled to said tracks for moving saidtracks on said bed toward or away from the direction of the trench beingcut,

a floating marine vessel coupled to said frame by a flexible umbilicalcable,

said vessel housing at least a prime mover and a hydraulic pump forenergizing said hydraulic motor; sensor means coupled to said rollermeans for monitoring the position of said frame relative to saidpipeline,

monitoring means adapted to be positioned on said vessel and connectedto said sensor means, said monitoring means being responsive to thesignals produced by said sensor means for providing an indication of theposition of said frame relative to said pipeline; and

said track means being remotely operated from said vessel in dependenceon said monitored signals received from said sensor means.

17. The system of claim 16 and further including:

at least another axially extending support arm,

-movable coupling means coupling said another arm to said frame forselectively moving said another an'n relative to said frame,

' means movably interconnecting said arms for selective movement of saidarms away from and toward each other, and

least another rotatable cutter means extending downwardly from saidanother arm.

18. The system of claim 17 wherein each cutter means comprises a tubularmember from the outer periphery of which outwardly extend generallyC-shaped blades.

19. The system of claim 17 wherein said roller means are movablysupported on said frame, and

movable means coupled to said frame for selectively positioning saidroller means on said frame relative to said pipeline.

20. The system of claim 19 wherein each of said cutter means isdetachably secured to its corresponding arm.

21. The system of claim 20 wherein said tracks are detachably coupled tosaid frame.

1. In a trenching system for cutting a trench in the bed of a body ofwater and including: a frame, ground-engaging means coupled to saidframe and adapted to move on said bed, at least one axially extendingsupport arm, movable coupling means coupling said arm to said frame forselectively moving said support arm relative to said frame, and at leastone rotatable cutter means extending downwardly from said support arm,the improvement comprising: hydraulic power means including a primemover, a hydraulic pump, at least one hydraulic motor, a hydrauliccircuit operatively coupling said pump to said motor to energize saidmotor with hydraulic fluid, means coupling the output shaft of saidmotor to said cutter means to rotate said cutter means when said motoris energized, and control means responsive to the pressure in thehydraulic circuit for automatically adjusting the power output of saidmotor.
 2. The system of claim 1 wherein said motor is a piston-typemotor having a speed control element, said control means is coupled tosaid speed control element to automatically vary the speed of said shaftin accordance with the variation in the amplitude of said pressure, anda floating marine vessel housing at least said prime mover and saidhydraulic pump, said pump being coupled to said frame by a flexibleumbilical cable.
 3. The system of claim 4 wherein said ground-engagingmeans include: a pair of self-propelled tracks, and at least onehydraulic motor coupled to each track for moving said tracks,independently or simultaneously, on said bed toward or away from thedirection of the trench being cut.
 4. The system of claim 3 wherein saidframe moves over a pipeline and further including: roller meansrotatably supported on said frame and adapted to rollingly engage saidpipeline at horizontally spaced locations for guiding said frame on saidpipeline.
 5. The system of claim 4 and further including: sensor meanscoupled to said roller means for monitoring the position of said framerelative to said pipeline, and monitoring means adapted to be positionedon said vessel and connected to said sensor means, said monitoring meansbeing responsive to the signals produced by said sensor means forproviding an indication of the position of said frame relative to saidpipeline.
 6. The system of claim 5 wherein said ground-engaging meansinclude self-propelled track means remotely operated from said vessel independence on said monitored signals received from said sensor means. 7.The system of claim 6 wherein said cutter means extend downwardly at apredetermined depth below said ground-engaging means whereby forwardmotion of said frame causes said cutter means to cut a trench in saidbed.
 8. The system of claim 7 and further including: at least anotheraxially extending support arm, movable coupling means coupling said armto said frame for selectively moving said support arm relative to saidframe, means movably interconnecting said arms for selective movement ofsaid arms away from and toward each other, and at least anotherrotatable cUtter means extending downwardly from said another supportarm.
 9. The system of claim 8 wherein said frame extends rearwardly ofsaid cutting means and is adapted for motion along said pipeline, andpivot means carried on said frame for imparting pivotal motion to saidarms about a generally horizontal axis.
 10. The system of claim 1wherein said ground-engaging means is a skid adapted for slidingmovement on the surface of said bed.
 11. The system of claim 1 whereinsaid cutter means comprises a tubular member having outwardly extending,generally C-shaped blades thereon.
 12. The system of claim 13 whereinsaid blades are in the form of scoops.
 13. The system of claim 4 whereinsaid roller means are movably supported on said frame, and means forselectively positioning said roller means on said frame relative to saidpipeline.
 14. The system of claim 11 wherein said cutter means aredetachably secured to their respective arms.
 15. The system of claim 14wherein said tubular member is hollow and further including:high-pressure water means connected to said tubular member to facilitatethe trenching operation.
 16. A trenching system for cutting a trench inthe bed of a body of water including: a frame for moving over apipeline, roller means rotatably supported on said frame and adapted torollingly engage said pipeline at horizontally spaced locations forguiding said frame on said pipeline; ground-engaging means coupled tosaid frame and adapted to move on said bed; at least one axiallyextending support arm, movable coupling means coupling said arm to saidframe for selectively moving said support arm relative to said frame; atleast one rotatable cutter means extending downwardly from said supportarm; said ground-engaging means including: a pair of self-propelledtracks, at least one hydraulic motor coupled to said tracks for movingsaid tracks on said bed toward or away from the direction of the trenchbeing cut, a floating marine vessel coupled to said frame by a flexibleumbilical cable, said vessel housing at least a prime mover and ahydraulic pump for energizing said hydraulic motor; sensor means coupledto said roller means for monitoring the position of said frame relativeto said pipeline, monitoring means adapted to be positioned on saidvessel and connected to said sensor means, said monitoring means beingresponsive to the signals produced by said sensor means for providing anindication of the position of said frame relative to said pipeline; andsaid track means being remotely operated from said vessel in dependenceon said monitored signals received from said sensor means.
 17. Thesystem of claim 16 and further including: at least another axiallyextending support arm, movable coupling means coupling said another armto said frame for selectively moving said another arm relative to saidframe, means movably interconnecting said arms for selective movement ofsaid arms away from and toward each other, and at least anotherrotatable cutter means extending downwardly from said another arm. 18.The system of claim 17 wherein each cutter means comprises a tubularmember from the outer periphery of which outwardly extend generallyC-shaped blades.
 19. The system of claim 17 wherein said roller meansare movably supported on said frame, and movable means coupled to saidframe for selectively positioning said roller means on said framerelative to said pipeline.
 20. The system of claim 19 wherein each ofsaid cutter means is detachably secured to its corresponding arm. 21.The system of claim 20 wherein said tracks are detachably coupled tosaid frame.